The hydraulic oil cylinder is a component widely used in the construction machinery, and during the working process of the hydraulic oil cylinder a piston needs to reciprocate continuously. When a piston rod extends to a limiting position, a piston end cap may be impacted strongly by a piston end surface, which may cause damage to the hydraulic oil cylinder. Therefore, a buffer device needs to be provided at that position to avoid the damage to the hydraulic oil cylinder caused by the above impact.
There are great differences among the existing buffer devices according to different applications and different sizes of the hydraulic oil cylinders. A compression spring can be used directly as a buffer device in a small-sized oil cylinder, however, in the hydraulic oil cylinder with a large cylinder diameter and a long stroke, if the compression spring is used as the buffer device, it is hard to obtain a spring having sufficient elasticity, and because that the pressure in the hydraulic oil cylinder is great, the spring will be damaged soon because of being repeatedly compressed. Therefore, the hydraulic oil cylinder with a large cylinder diameter and a long stroke generally use a hydraulic buffer mechanism shown in FIG. 1.
Referring to FIG. 1, the buffer device includes a small buffer ring 06, being mounted in an intermediate annular groove arranged on a piston rod additional section, and a small buffer sleeve 04, being sleeved on the piston rod additional section. Corresponding to the small buffer sleeve 04, a buffer inner hole 07, having an inner diameter cooperating with an outer diameter of the small buffer sleeve 04, is provided at a cover opening portion of a rodless cavity end cover 01 of the oil cylinder. When the piston rod is retracted, the small buffer sleeve 04 is firstly inserted into the buffer inner hole 07 to block an oil-returning oil passage of the rodless cavity in a cylinder barrel 02, and at the same time, a throttling oil channel is formed by a gap between the small buffer sleeve 04 and the buffer inner hole 07; so that, the piston 05 can continue to move in a retracting direction, however due to a buffer effect of the throttling oil channel, the movement speed of the piston 05 is slowed down. And when the piston 05 gradually approaches an end position of the retraction process of the piston rod 03, the throttling oil channel between the small buffer sleeve 04 and the buffer inner hole 07 is gradually increased, which gradually increases the damping effect of the throttling oil channel, thus the movement of the piston 05 is gradually slowed down until eventually reaching the end position of the retraction process of the piston rod 03 smoothly.
Currently, the above buffer mechanism is widely used in the hydraulic oil cylinder with a large cylinder diameter and a long stroke to provide a better buffer protection for the hydraulic oil cylinder.
However, the above buffer mechanism also has some obvious disadvantages. Firstly, for the hydraulic oil cylinder with a large cylinder diameter and a long stroke, such as a driving cylinder used for driving a digging arm of an excavator, the hydraulic oil cylinder is generally working in a working condition of huge load and high frequency. In such a case, the small buffer sleeve 04 in the above buffer mechanism needs to repeatedly insert into the above buffer inner hole 07 at a high speed, and because that the fitting interspace between the small buffer sleeve 04 and the buffer inner hole 07 is very small and the piston rod 03 is very heavy, the piston rod 03 is easy to be tilted to one side under the action of gravity. Therefore in the above hydraulic oil cylinder, failures of the buffer mechanism that the buffer sleeve 04 fails to insert into the buffer inner hole 07 are very easy to happen, which may cause the entire hydraulic oil cylinder being not able to operate normally.
Another key problem of the above buffer mechanism is that, the outer diameter of the small buffer sleeve 04 must fit with the inner diameter of the buffer inner hole 07 precisely, otherwise the buffer effect may not be achieved, thus the buffer mechanism has an extremely high manufacturing precision requirement which is hard to meet for manufacturers with ordinary manufacturing level. Due to the excessive high manufacturing precision requirements, the hydraulic oil cylinder with a large cylinder diameter and a long stroke has become a bottleneck problem for producing construction machineries such as excavators, which severely restricts the production capacity of the manufacturers in downstream production chain.